The invention relates to a patellar saw guide which has a plurality of rotatable teeth adapted to engage an edge of a patella prior to its preparation for receiving a prosthetic implant.
A patellar clamp and saw guide are used during a total knee arthroplasty procedure to prepare the posterior surface of a patellar bone to accept a prosthetic implant.
Typically, a surgeon will select a patellar prosthesis for implantation either by utilizing a resurfacing technique wherein the prosthetic patella will be resected and resurfaced and/or by an insetting procedure where the prosthetic patella is inserted into the prepared surface of the patella.
The patella is a sesamoid or lens shaped bone which slides in a groove between the condyles of the femur. Its function is to increase the efficiency of the quadriceps muscle by shifting the line of action of the muscle's pull forward. As the knee articulates, the muscles and tendons force the patella toward the condyles of the femur. Consequently, there is considerable relative motion between the patella and the other bones comprising the knee joint.
Because of aging or disease, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to surgically remove the condyles and replace these structures with prosthetic implants. By the same processes, the articulating surfaces of the patella may also degrade. In connection with the implantation of a prosthetic knee, therefore, the articulating surface of the patella may also be replaced. Because of the tendons connected to the patella, it is generally advisable to replace only the articulating surfaces. An ultra high molecular weight polyethylene articulating surface, with or without a metal baseplate or metal backing, will be implanted on the posterior side of the patella, adjacent the femoral condyles.
In either a total resurfacing procedure or a patella insetting procedure, it is important that a sufficient amount of bone stock remain after resection to accept the typical fixation pegs of the patellar prosthesis and maintain the integrity of the remaining patellar bone. Therefore, proper location of the saw blade is important.
As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.
Prior art devices for aiding the surgeon in performing patella resections are well known to those skilled in the art. For example, Peterson, in U.S. Pat. No. 4,673,862, teaches a method and instruments for the installation of a patella button prosthesis which involves performing a patella resection.
In particular, Peterson relates to a saw guide which comprises a pliers-like instrument having a pair of mutually pivotable jaw members. The jaw members are designed so as to enable them to surround part of the outer periphery of the patella with each jaw member having a respective handle, integrally formed therewith, which handles may be pivoted so as to pivot the jaw members to and from engagement with part of the patella periphery. The Peterson device requires that a flat saw blade be guided over the face of the jaw members after the patella has been set to the correct depth between the members.
U.S. Pat. No. 5,147,365 relates to a patella osteotomy guide in which the jaw members include a slot for guiding the flat saw blade and an arm for setting the saw blade depth in the patella.
U.S. Pat. No. 5,486,177 relates to a patella milling instrument having a clamp which contacts the underside of the patella. A similar clamping tool is shown in U.S. Pat. No. 5,284,482.
U.S. Pat. No. 5,222,955 relates to a reaming system designed to cut a conical bore in a patella surface while the patella is being held in a patella clamp similar to that disclosed in U.S. Pat. No. 5,284,482. U.S. Pat. No. 5,941,884 relates to a patella clamp which includes indicia of both the amount of bone resected and the amount of bone remaining.